


Rock Bottom

by Biracial_Mermaid



Category: Gravity Falls
Genre: A lot of self deprecating thoughts, Angst, F/M, Future time setting, Kind of a slow beinning, M/M, Shapeshifting, Smut, This is the fic that's going to send me to hell tbh, Unrequited Love, awkwardly written smut, man i'm just hella bad at writing vaginas, one sided Incest
Language: English
Status: Completed
Published: 2015-04-14
Updated: 2015-04-14
Packaged: 2018-03-22 15:44:23
Rating: Mature
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 5,453
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/3734395
Author URL: https://archiveofourown.org/users/Biracial_Mermaid/pseuds/Biracial_Mermaid
Summary: <blockquote class="userstuff">
              <p>You think you have problems? Dipper Pines is in love with his twin sister, which is a problem within itself. Bill shows up out of nowhere and warns that he's headed towards a downward spiral because of his feelings, but what does the omnipotent demon know, right?<br/>The events that follow are more or less entertaining (to Bill, at least.)</p><p>((I'm so fucking gross holy shit))</p>
            </blockquote>





	Rock Bottom

**Author's Note:**

> I'm going to hell for this fic, I just know it.  
> Hope you like sad boys and heartless triangle demons!

There used to be a time when Dipper Pines welcomed the morning, pleased with his life and eager to see the face that almost mirrored his own. Sometime around their thirteenth year of life together, Mabel’s face in the morning became better than whatever dreams he’d had during the night, leaving him eager to welcome the sun and his family. She often complained about her braces, or how frizzy her hair was in the humidity of a Pacific Northwest summer and Dipper wanted nothing more than to tell her that he loved the metal over her crooked teeth, or that her brown hair was absolutely gorgeous with each curled, frazzled strand that he itched to tuck behind her ear. Of course, with each suggestively romantic thought, he felt sick with himself and stayed silent on the matter aside from the occasional compliment.

Each day wagered a war on his own mind, one in which he’d question himself, his sanity. You should _no_ t be looking at your sister like that. You should _not_  think about how pretty her lips are. You should _not_ check her ass out each time she bends over. Each summer was spent in Gravity Falls, and it was a nice distraction during the day as he would work with Soos and Wendy, laughing at things found on the internet and muttering impressions of customers beneath their breaths. Each night, however, was torture as he fought to clear his head, every once in a while glancing at his sleeping sister just mere feet away.

Eventually, he began to grow up, and so did Mabel. Her waist began to synch in just the right places, her hips filling out just the right way and while her sweaters could hide those attributes, they couldn’t hide the perky breasts that had seemingly appeared overnight, leaving him with the need for more distraction. Unfortunately, Wendy grew up too, and eventually left for college. Soos got married and spent more time at home with Melody. Dipper’s distractions were gone when he needed them the most.

When he was 17, the need for distraction grew so largely that Dipper made the decision to move in with Stan year-round. His decision wasn’t due to just that _one_  problem, but it certainly did fill him with less anxiety to know he wouldn’t be waking up to greet the morning all too enthusiastically anymore; he wouldn’t have to repeatedly beat himself up and think about how fucking _s_ _ick_ it was to want to kiss his own sister, his _twin_ at that. He’d promised to finish his last year of high school at Gravity Falls High, then to look into colleges somewhere in the middle so he could travel back and forth freely.

He moved all of his belongings into the attic of the Mystery Shack, both haunted and relieved by the empty bed across the room. He babysat Soos’ kid when he was asked. He even got drunk with Wendy a few times and diligently listened to her stories of college, and her reason for dropping out to move back home. He realized that she didn’t make his heart beat as fast anymore, that he had grown out of his crush on the gorgeous redheaded girl with perfect teeth. She was just a friend to him now; and whether that was okay or not given his feelings for Mabel really grated on his mind.

For a month, the small town life was perfect, though he really did miss his siter. They would Skype sometimes, and his heart would break a little each time she complained about how much she missed him. His stomach would leap with joy each night she suggested they just sleep on camera together. A month, he was happy with his life, ready to start forgetting about the fact that he spend a small handful of years crushing on his own sibling.

As with anything in Dipper’s life, though, the perfect harmony didn’t last. It’s eerie, sometimes, how the universe can lay things out in chronological order. One minute, Dipper found himself humming along to the shop speakers as it belted out that one song by &ndra that Mabel had gotten him to sing with her and Stan during the zombie outbreak. He smiled at the memory, thinking about how slow it was in the store today; if he wanted he could just grab his laptop and call her on Skype, say he missed her and just marvel at her beautiful face. Then, the next minute, his perfect, happy life was shattered and enlightened all at once as the bell over the shop’s door jingled.

It was a happy reunion for the twins, with a lot of hugging and understated “I miss you”s, and despite the excited grin overtaking both of their faces, Dipper had sobered considerably when Mabel stated she was moving in with him and Stan. Once more, Dipper’s mornings were ruined with how excited he was for them.

The first change took place when Mabel straightened her hair one day in October and pinned it to her head. Dipper’s gaze scanned the pale flesh of her long, elegantly thin neck, tucking away the memory of her bare, slender shoulders and the way the pink dress hugged the curve of her waist before poofing into a mess of tulle that showed her perfect legs; that looked more like they’d been carved from marble than flesh and bone. She was talking, Dipper noted. _I should probably listen to her instead of stare like a creep._

“I really don’t know why you’d miss out on homecoming willingly! You don’t _have_ to have a date, Dipper, it’s not _prom_ or anything. I’m going with Grenda and Candy, you can definitely come with us if you want instead of reading some dumb old book.”

“This dumb old book,” he protested as he motioned to the expensive binding. “Is a classic, and worth more than half my grade this semester.”

“But homecoming is so important, Dipper,” Mabel whined, pulling a pair of silver peep-toe pumps onto her feet. For the slightest moment, Dipper thought about how he’d love to see her in nothing _but_ those shoes. _God, I’m fucked up. What is -with- me tonight?_  “As soon as you miss it, you don’t get it back! It’s essential, Dipper, essential,”

“I still think I’ll pass. Partying has always been more your scene, anyway.” There was no malice in his tone as he stated the simple fact that she’d always had more fun during large events than he did.

With a small pout, Mabel nodded and bounced over to Dipper’s bed, pressing a kiss to his cheek. “I’ll be back in a few hours,” she informed him, grinning at the bright red lipstick mark left on his cheek. “After the dance we’re all going to Pacifica’s for the after party.”

Picking his book back up so as to tear his gaze from Mabel’s cleavage, he replied. “That’s fine. I’ll probably be asleep by the time you get back, anyway.”

“Alright, then, don’t wait up. Love you, bro-bro!” she called, hurrying to the stairs. He replied that he loved her too, and only moments later he heard a car pulling out of the gravel parking lot in front of the shack, leaving him alone with his thoughts.

 _You’re fucking sick,_ he thought to himself, too disgusted to focus on the words of his book. He gave up after rereading a sentence four times and tossed the hardback onto the ground between their beds. _Your own sister… If she knew, she’d never even speak to you again. Fucking psycho._

“You got that right, Pinetree! You‘re all sorts‘a fucked up!” A voice cut the silence of his room. Suddenly put on edge, Dipper sat up in bed and looked around frantically. That voice… He knew that voice. It haunted his nightmares until he was old enough to convince himself that of all the strange things in Gravity Falls, that thing- whatever it was- wasn’t going to make itself apparent to him again.

“Bill?”

“You guessed it, kiddo,” The echoing voice had taken form right beside Dipper without him noticing, causing the teen to jump to his feet as the triangle spoke. “Though, you’re all grown up now. Guess I can’t call you that,”

“Where did you come from?!”

“The depths of hell, Pinetree. Remember, that whole ‘demon’ thing? Duh! We have a habit of showing up when people hit their lowest and kid, lemme tell ya, your lowest is on it’s way~”

Arching an eyebrow incredulously, Dipper stares at the tiny form sitting on his bed, seemingly inspecting his nails. “What does that mean?”

“I mean just what I said. You’re on a one way train to rock bottom with no escape route and you aren’t gonna realize ‘til it’s too late! Boom! Crash!” The demon erupted into a fit of hysterical cackling, earning him a horrified stare from the brunette teenager.

“Shut up!” Dipper finally yells when he comes to his senses. “Just- just shut up! My life is fucking fantastic right now, I’m at a comfortable place in my life and-”

“Don’t give me that stupid ‘I’ve reached nirvana’ bullcocky, Pinetree, I heard exactly what you’ve been thinking about your sister,” Dipper blinks once and sees himself sitting on his own bed, pupils narrowed into tiny slats. It isn’t _really_  himself, though the image is uncanny. “ ‘Oh poor me, I want to fuck my own sister! I’m such a narcissist that I want to take my twin and bend her over and-’”

“That’s enough!” Dipper interrupted. “Get out of my room!”

Other-Dipper huffed and once again, became a demonic triangle leaning back on the other’s bed. “Fine,” he grumbled, seemingly unimpressed with the turn of events. “But just know that I  _am_  going to be here when you break.”

And then he was gone.

Yes, that was a night of firsts. It was the first time that Dipper was visited by Bill in years. It was the first night that his sister comes home drunk and slurring her words, crawling into bed beside Dipper. It’s the first night that she shushed him and told him that he shouldn’t worry, that Mabel’s here and she’s got him, and he’s got nothing to worry about, leading him to foolishly disregard Bill‘s warning in favor of pressing his face into the crook of her shoulder and savor the sweet smell of vanilla and cherries. It’s also the first night that Mabel falls asleep in his arms, muttering about a boy she’s going on a date with tomorrow.

A couple months later, during the first snowfall of the season, Dipper found himself pulling a pair of gloves onto his chilled fingers as the sound of footsteps came clomping up the stairs. “Mabel!” he greeted, tossing a grin over his shoulder. “Snowball fight?”

“Can’t, Dip, I’m going out with Keegan. Again. I know, I know, hold your applause,”

“Oh. Right. Why’d you come up here, then?” he asked, tipping his head to the side. He watched Mabel’s face shift from delighted, to uncomfortable then bashful and thought that there was nothing more he’d like to do than kiss the expressions away until nothing was left but pure joy.

“Well,” she began, pursing her lips to the side. “I was thinking of moving into the spare room, the one we fought over the first summer we spent here. You’d be cool with that?”

Though Dipper felt his heart drop the slightest bit, he nodded (perhaps a bit too enthusiastically). “Yeah, sure, yep-hm! I mean, why would you, though? I mean- what made you think of it so suddenly?”

“I just feel like we’re old enough to sleep in different rooms and stuff. Besides,” she paused, averting her gaze from her brother. “Keegan and I wanted to… I mean… I just think it’d be awkward for me to do it in a room I share with my brother, ya know?”

“Do- uh… Do what?” Dipper asked through a dry throat and knotted stomach. Again, Mabel looked bashful.

“Lose my vi-” She was cut off by a horn honking in the driveway, followed by a snowball hitting the pane of their triangular window. “Ah, you’ll figure it out, you’re smart! I’ve gotta go, fun dip. Deuces-”

As Mabel practically fled the room, Dipper forced a laugh and sat down on his bed. “Ha, yeah. Dice and… all that…” With a sigh, he laid on his back and glared up at the ceiling.

_You shouldn’t be jealous. She obviously wouldn’t have given it to you anyway, you piece of-_

“Pine tree, long time no see!” Bill cheered as he leaned over Dipper’s head, alarming the boy slightly. “Oh jeez, you don’t look happy to see me. What, is it the hat? It’s the hat isn’t it?”

“You’ve worn the same hat literally every time I’ve ever seen you,” the brunette replied, narrowing his eyes. “Any reason I’m not happy to see you has _nothing_ to do with your stupid hat.”

“No no _no_ , Dip for brains, I own a bunch of black top hats! They all fit differently, though and-”

“Look, I’m not really in the mood today, alright?”

“Oh trust me, man, I _know_. I saw that little stint there with your lady friend, fun dip.”

“My lady friend? You mean my sister?” Dipper asked, furrowing his eyebrows together as he sat up and turned to look at Bill.

“Yeah, shooting star! Man, she grew up really, _really_ nicely, don’t you think? I mean have you seen her ti-”

“Do _not_ finish that sentence.” Dipper growled, hunching over defensively. “Why are you here? Is this me hitting rock bottom like you said?”

“This? Oh god no. Don’t worry, there’s still more to come! I just thought I’d come by to check on ya! Can’t be easy, wanting to bang your sister, though I totally understand, she’s got a great ass.” Sometime during that tryst, Dipper had lunged at the demon, angered by the fact that he talked about Mabel so objectively, that he talked about her at all; that he voiced something about Dipper that the brunette would never admit out loud.

“Calm down, kiddo, just stating the facts!” Bill laughed from somewhere behind Dipper, who was currently frowning so deeply that his jaw began to ache. “I should get going, but I really enjoyed the chat, Pine tree. I’ll see you around!” With that, Bill disappeared in a quick flash of light, like the shutter from a camera.

Dipper worried for himself, finally realizing what Bill had been trying to tell him; that Bill had been taunting him with the promise of inevitable disgrace, but if it wasn’t coming at the hands of Mabel losing her virginity to some blonde haired douche bag, what could be so bad that it leads him to finally breaking? The gravity of the situation ate at his stomach, making him feel sick with anxiety.

The general apprehension faded over the course of a few months until the only discomfort he felt was the usual feelings he had around Mabel, diluted with pure jealousy when Keegan was around. He had to get used to it though, had to condition himself into smiling every time Keegan told a joke or Mabel stole a kiss from the lips he would kill to switch places with.

Dipper wondered if they’d be broken up by graduation. Call him fucked up, but he kind of wished for it. He wanted nothing more than for Mabel to storm through his bedroom door with tears streaming down her face, pouring from her beautiful green eyes. He’d kiss them away and pull her into his lap, all the while whispering that Keegan was an idiot. He wanted her to come running to him, and the more he wanted it the more disgusted he felt with himself.

Graduation came and went, though, and once again, Dipper found himself lounging on his bed as Mabel asked if he was _positive_ he didn’t want to go to Vegas with her friend group. “It’ll be a road trip!” he gushed, shoving a handful of tank tops into her suitcase. She’d since stopped wearing those sweaters and opted for more form-fitting garments, much to Dipper’s aroused discomfort. “Come on, Dip, I miss you.”

“Miss me? I’m right here, Mabes.”

“Well yeah, but…” She paused and sighed, shaking her head. “Nevermind, it’s stupid. No, never mind, I have to say it. Dipper, you’re like… You’ve been really weird lately!”

“You always used to call me weird, I don’t think it’s anything particularly new.”

Mabel looked as though she was about to answer, but ultimately decided against it. “Yeah,” she huffs, shutting her suitcase. “I’ll be back in a few days, okay?” The lowered tone in her usually excitable voice is one that had Dipper’s heart breaking. Before he could bring himself to apologize, though, she’s gone, tugging her suitcase downstairs and greeting Keegan with an excited gasp of his name.

He doesn’t speak to Mabel for the week she’s out of town, and that isn’t due to lack of trying. He texted her once or twice, sent her messages on various social media outlets, and yet didn’t receive any sort of indication that she’s alive aside from the numerous selfie posts of her, Candy, Grenda and Keegan as they did stupid things together. For a week straight, he would feel as though his stomach was dragged through gravel. He even told Stan that he wasn’t in the mood to work, and did nothing but angrily walk the forest, wondering why he didn’t just _go_ with them when Mabel offered.

The day she got back, Dipper found himself being pulled into an enthusiastically tight hug; which he happily melted into. Arms tight around Mabel’s waist, face nuzzled into her neck, he let out an almost relieved sigh. “I missed you,” he breathed.

“Missed you too, Dip,” she muttered, fingernails comfortingly grazing the spot between his shoulder blades. When she finally pulled away, there was a grin on her face. “Hey, can I tell you something I’ve been _dying_ to tell you? Like seriously, I’m dead,” she sang before making a gagging noise and grabbing her neck.

“You _know_ how much I hate hearing you talk,” Dipper laughed, sitting on his bed. “But go ahead.” His eyes peeked up at Mabel, whose hands tangled in his as she stood before him. He thinks about how giddy she looks, grin on her face, teeth sinking into her plump bottom lip. _I could kiss her,_ Dipper thought to himself. He was half tempted to do it, to pull her down to his level and connect their lips. She would melt against him and sigh with delight and-

As he squeezed her hand impulsively, something didn’t feel quite right. Pulled out of his daydream, his adoring gaze shifted to their interlocked hands; and oh god he might be sick. “W- what’s this ring?”

“I’m officially a married woman!” Mabel all but cheers, bouncing in place in front of Dipper. “I’m not Mabel Pines anymore- say hello to Mrs. Mabel White! Isn’t it pretty?!”

His face paled as he looked at the ring, as it glistened in the sunshine streaming in through the window behind them. “I… When?”

“Our last night in Vegas. Oh man, let me tell you about it-” He really didn’t want to hear it. He wanted to pull a pillow over his ears and block out every detail she was about to recall, but despite how badly he wanted to, he let Mabel talk. The fact that he felt as though he couldn’t move had little to do with it. “We paid some dude like twenty bucks to buy us a bunch of liquor, since we had the money left over. Now, I’m no lightweight, you know that, but I got so trashed that we all decided one of those quickie chapels was a good idea and- well- that happened and now I’m married so-”

“Mabel!” Dipper interrupted. As he realized what that meant; what a drunk marriage usually entailed. “We can go to the courthouse and get it annulled!”

“Wha-”

“There isn’t a lot of time, they’re closing in a half an hour, come on!” he hurried, jumping up to take her hand. “I knew you liked having fun and all but getting tossed and marrying someone is pretty hard core.”

“Dipper, I-”

“But still, mistakes happen and it’s totally okay! I just-”

“Diiiiip-”

“Mom and dad don’t even have to know, we can-”

“Dipper!” Mabel finally yelled, snatching her hand away from her twin. _Oh no…_ Dipper dreaded what was about to leave his sister’s mouth. He turned slowly, eyes wide as his gaze fixed on the girl with a guilty gaze directed at the floor. “Dipper I… I really love him. I think I want to stay married.”

“Mabes… Come on, you’re only 18,” he pled, voice cracking the slightest bit. “Don’t do anything stupid.”

“It’s not stupid,” she protested, still looking anywhere besides her brother. “He’s just what I want to wake up to every morning. He laughs at my jokes and lets me tell him all the stories of us growing up- even the spooky stuff from Gravity Falls! He makes me feel weird and out of place- but that’s okay because he is too; and if he’s not normal then I don’t wanna be either!” She took a breath and finally brought her eyes to Dipper. “He reminds me so much of you.”

Dipper can’t think of a way to argue that, despite the feelings raging inside of him, so intense that he can’t identify them. He wanted to scream and tell Mabel that if she wanted to be with someone like Dipper she could just be _with_ Dipper. He wanted to grab her shoulders and shake, all the while exclaiming that she’s too young to be married and that she’s going to ruin her life if she doesn’t divorce Keegan.

But he didn’t.

In the end, Dipper could do little more than stand at the entrance of the attic, eyes glued to his shamefaced sister. “You’re right,” he finally breathed. His voice was little higher than a whisper, prompting him to repeat himself in a more firm, determined voice with a forced smile. “You’re right, Mabes. I’m really happy for you.”

The grin that spread across her face was more than thrilled and she surged forward, arms flinging around Dipper. “Thanks, bro-bro. Hey, when you find the girl of your dreams let me know, I want to be able to give a matchmaker speech at your wedding!” she chirped, reaching up to tousle his hair. He forced a smile at the playful action, and chuckled as though his chest wasn’t painfully collapsing on itself. “I’m gonna go pack up my room and go back to Keegan’s.”

“You’re moving out already?” The thought made Dipper’s chest ache worse.

“Yep!” she replied, all too happy as she took the first couple of steps down the stairs. “What, you didn’t expect me to stay here for the first few days of my honeymoon, did you?”

“Course not,” he replied, rolling his eyes, false smile plastered on his cheeks. “Go on, go get your stuff ready. I’ll see you the next time you come to visit.”

“Or just come visit us whenever we get a place!” she called behind her, already halfway down the stairs. “Bye, Dip!”

Dipper did little more than wave in response, though he was fully aware Mabel didn’t see. Less than an hour later, he watched from the attic window as Keegan’s car sped off with Mabel in the passenger seat, arm hanging out of the window.

 _You lost her,_ he thought silently. Before he knew it, he was on the ground, knees pulled to his chest. S _he was never going to be yours, but now she’s gone forever. She’s married and soon enough she’s going to have blonde babies that look like *him*. She’s gonna ask why you aren’t married yet and you aren’t going to have the balls to tell her; and if you do she’ll never speak to you again._ By the time he finished his internal soliloquy, his face was buried between his knees, dark blue denim jeans soaking the tears from his eyes. _You sick, disgusting piece of shit._

“So, married, huh?” The question was followed up by a low, amazed sounding whistle. “Gotta be hard, watching your sister drive off with blondie.”

“Fuck off,” Dipper barked, lifting his head to glare daggers in Bill’s direction. Why was it that whenever something big happened, _he_ showed up? “I’m not in the mood.”

“Not in the mood? ‘Course you aren’t, kid!” he replied. Dipper wore the tone floated on bubbling laughter. “You watched your sister totally abandon you for that dork, then just toss you to the side while she got married. Tell me, Pinetree, do you think if you’da gone like she asked, would she be married right now?”

“Shut up!” Dipper finally yelled, snapping at the triangle. The brunette stood, sat on his bed and wiped his tears. “Just- just shut up.”

“Dang, if I’d have known I touched a nerve…” _His voice is too empathetic..._  

“I would have said something sooner!” _There it is,_ Dipper thought as the demon erupted in a fit of laughter.

Dipper turned away, laying on his side to face the wall away from Bill. After a moment, the laughter died down, leaving the room silent. Dipper hoped that the triangular douche bag had left, but felt a hand on his side.

“Dipper,” Okay, that was _not_ Bill’s voice. Sitting straight up, he spun his head around to look at the mess of bright orange hair and pale freckles.

“Wendy?”

“Sorry you’re feeling down,” she murmured, moving her hand down to his thigh. As she spoke, her voice echoed against itself and it sent shivers down Dipper‘s spine. “Maybe I can help make you feel better?”

“Get off,” Dipper demanded, shoving the hand off of his leg. “I already told you I’m not in the mood to deal with you.”

“Right,” ‘Wendy’ said, speaking in Bill’s voice. The hand crept closer again, though it didn’t replace itself on Dipper’s body, but rather behind him. Wendy’s face inched towards his own until it wasn’t Wendy’s at all anymore, but rather Mabel’s. “I forgot. You‘d prefer _me_ over _her_. Wouldn‘t you, Dipper?”

Their lips were almost touching, and they probably would have been if Dipper’s hadn’t curled back in striking anger. “ _Bill_ ,” he hissed, eyes narrowing into slits. “I’m warning you, get-”

“Oh come on, Pinetree!” Mabel giggled, bringing ‘her’ legs forward to straddle Dipper’s slender waist. “Take it all out on me. All the anger, all the frustration… You know I should be with you instead,” she cooed, lips ghosting a breath over the skin of Dipper’s neck. “Show me why.”

That does it. That’s what makes Dipper snap. In a moment, he had the Bill-Mabel monstrosity pinned to his mattress, hips pushing against her innermost thighs. The thing lets out a delighted chuckle and casts those perfect green eyes towards Dipper- those green eyes that were almost Mabel’s. “Piece of shit,” Dipper growled as his fingers twisted into the fabric of Mabel’s- Bill’s- sweater. “You’re such a piece of shit to do that.”

Another giggle as their hips met, creating a friction against Dipper’s already half-hard cock. “You’re not still dressed are you? Hurry up and f-”

“Shut up!” Dipper interrupted, yanking the skirt from the perfectly sculpted hips beneath him. Miraculously, as soon as it’s gone, every other article of clothing is too, much to his confusion. “What? How did you-”

“Magic, Pinetree, remember?” The tone is so condescending, so patronizing and spiteful, that Dipper can’t help but grow even more irritated. He forced what _should_ have been Mable’s legs apart and pretending not to glance at the almost _too_ perfect shade of pink previously hidden by the flesh of her thighs. It distracted him as he thought, _I wonder if this is what the real Mabel looks like, or if this is part of Bill’s own design._  “Hurry up and quit staring, will ya?”

Right. He’s angry at the being beneath him. He’s angry that Bill manipulated him this far, angry that it isn’t really Mabel, angry at himself for being angry. There’s so much anger that he can hardly see straight, and it only flared up more as he forced himself inside of his twin’s doppelganger with a low, growling groan.

Warmth enveloped his dick, wet heat clenched down around his sensitivity; and the moan that sounded from beneath him was almost unworldly. His hips snapped forward, drawing that perfect, breathy moan from the form beneath his body. “Faster-” Mabel’s voice hitched. “Don’t hold back.” As if to punctuate the point, a pair of legs tightened around Dipper’s waist and forced his hips forward. “Fuck me like you’d fuck her.”

At the mercy of a voice belonging to his sister, Dipper’s hips began to work on their own accord. He wasn’t fucking Mabel, he knew that, and that’s why his thrusts were so pointedly tough against the other’s; why the sounds leaving his throat weren’t moans at all but rather growls masked with profanity.

“Fuck,” the pseudo-girl gasps, head laying back. Brown curls are strewn to and fro, creating a halo around the face mirroring the girl he’d loved since puberty. The next word breathed from Mabel’s lips is what completely breaks him. “Dipper,”

The teenager can feel his hips slow the slightest bit before his head falls against the slender shoulder. “Ah,” he grumbled, slipping his eyes shut. “A- ah, fuck, Mabel.” Arousal and self-disgust twist in his stomach as he finally gives in, finally allows himself to think _this is Mabel._

Somewhere in the back of his mind, he wants to remind himself that his is Bill, that this is Bill with his sister’s face but for the most part, he allows his thrusts to speed back up against _Mabel’s_ because maybe if he believes it hard enough, it’ll be Mabel’s skin that he sinks his teeth into, Mabel’s moans that encourage his hips to go faster, harder, Dipper please _God_ harder!

Maybe if he believes it hard enough, the sick feeling in his stomach will go away and he won’t hate himself as much.

“I-” Dipper gasps, nails digging into Mabel’s waist as his hips frantically slam against hers. “I fucking- God, Mabel, _fuck_ ,” The only reply leaving her mouth is a moan as her nails bury into the flesh of his back. None of the thoughts crossing Dipper’s mind are intelligible, and most are profane, but all are centered around Mabel.

_She feels perfect,_

_I love hearing her moan my name like that,_

_I love her,_

No sooner than he thinks that does Mabel press her lips to his ear and breathe, “I love you,” in a needy whine, as if she knew just what he needed to hear. The tightness that had been building in his stomach released all at once in a wave of heat more intense than anything he’d felt before; reverberating all the way to the tips of his fingers knotted between the sheets.

It takes a moment for Dipper to realize what just happened from start to finish, and when it finally hits him the sick feeling he’d been repressing hits him full force. He’d fucked Mabel- no, he’d fucked _Bill_ to the thought of Mabel- and he’d only confirmed how twisted he really was. He’d been told with such conviction the words that he wanted to hear for years and now that he’d heard them all he wanted to do was puke.

Less than gently, he pulled out and leaned over the post of his bed, heaving bile into the wooden floor of the attic. Behind him, Bill- the real Bill- laughed in that annoyingly pleased voice of his. “Man, who knew baby’s first orgasm would make him puke!”

If his mouth wasn’t busy vomiting, Dipper would have hastily told him to shut up. The knuckles holding onto the footboard were white, his nails leaving scratch marks in the wood of the bed frame. “I- I-” he stuttered, shivering so heavily that the bed shook. Before he could finish, he gagged on his own words and got sick again, sparking another round of laughter from the demon who had since returned to being nothing more human than a pyramid.

“Told you that you’d hit rock bottom, Pinetree. I told you, and I told you that I’d be here for it. Now... How's about a deal?”


End file.
